1. Field of the Invention
The present invention relates to improvements in an apparatus and method for chamfering, for example, a semiconductor silicon wafer with loose abrasive grains.
2. Related Art
The periphery of, for example, a semiconductor silicon wafer (hereinafter referred simply to as wafer) has been chamfered, heretofore, in order to prevent dust generation when a wafer is supplied as a starting material for a highly integrated super LSI or to prevent chipping, flaking away and the like in a previous process thereof.
A recent chamfering process, for example, wherein high-precision mirror-polishing is performed, has been generally conducted stepwise in three steps of first, second and final. Such steps respectively correspond to the three steps of rough polishing, middle polishing and fine polishing in a polishing process on a major surface of a wafer. In the chamfering process, grinding with fixed grains, such as a grinding stone, are generally applied to the first and second steps and buff polishing is applied to the final step.
On the other hand, a method for chamfering a wafer by acid etching with a hydrofluoric/nitric acid-base etchant is known other than the above mentioned grinding and polishing using abrasive grains. The acid etching method has a fault that it is difficult to control a profile of a chamfer. Therefore, fixed abrasive grains are generally used in the first and second grinding steps in order to solve the fault.
However, when fixed abrasive grains are used in the first and second steps, cracks in a crack layer (damaged layer) produced in the surface region of a ground surface show a large degree of dispersion in penetration depth if they are examined microscopically, which is, with the naked eye, observed as a striation pattern of a surface roughness on a main surface and causes non-uniformity in sectional profile of a chamfer. That is, the use of fixed abrasive grains wrongly affects dispersion of the quality. Diamond abrasive grains, which are generally used as fixed grains, have a problem that a crack layer locally penetrates to a depth and, as a result, dispersion in surface roughness produces a pattern of striation, too.
Many countermeasures, such as to process for a longer time with finer grains or to process in an increased number of steps, have been tried to minimize dispersion in penetration depth of cracks in the crack layer, but the trials have been failed owing to reduction in working efficiency and a wrong influence on productivity.
Under such circumstances, a processing technique has been desired, which gives less dispersion in penetration depth of cracks in a crack layer in each of the first and second chamfering steps, that is one which does not locally produce a crack or cracks with abnormally greater penetration depth than the rest has been desired. It is natural that improvement of working efficiency should be secured in the desired processing technique.